1. Field of the Invention
This invention pertains to welding machines, and more particularly to apparatus that feeds a weld wire in electric arc welding machines.
2. Description of the Prior Art
An important part of MIG welding machines is the mechanism that feeds the weld wire to the welding gun. The wire feeder mechanism must be able to handle different materials and sizes of the weld wire to suit the workpieces to be welded and the welding operations to be performed. Typical sizes of weld wires range from approximately 0.023 inches to 0.052 inches in diameter. Typical materials for the weld wires include steel, stainless steel, and aluminum.
The weld wire feeder mechanism typically includes a small electric motor with a speed reducing gear drive. A bore of a feedroll fits over an output shaft of the speed reducer. The feedroll has an outer circumferential groove sized to suit a particular diameter weld wire. In a typical prior weld wire feeder mechanism, a radial pin in the speed reducer output shaft coacts with a slot in the feedroll to rotate the feedroll with the shaft. The feedroll is axially held on the shaft by a small screw that threads into the end of the shaft. The screw head or washer overlaps the feedroll around its bore to hold the feedroll on the shaft. A pressure roller presses against the feedroll to form a nip through which the weld wire passes when the feeder mechanism motor is energized.
Prior weld wire feeder mechanisms work very well, and they have gained widespread acceptance. Eventually, however, the circumferential groove in the feedroll wears. When that happens, the feedroll must be replaced. To do so, the screw on the end of the speed reducer output shaft is removed. That task typically requires the use of a tool, such as a screwdriver or wrench. When using the welding machine in the field, the necessary tool may not be available. In addition, the screw and related components are susceptible to being dropped and lost.
Thus, a need exists for improvements in the feedrolls of welding wire feeder mechanisms.
In accordance with the present invention, a toolless feedroll for a welding machine wire feeder is provided that is more quickly and efficiently changed than prior feedrolls. This is accomplished by apparatus that includes a spring that urges a blind slot in the feedroll to engage a radial pin on a shaft.
The shaft extends from a housing that is part of the wire feeder. The radial pin is located close to the free end of the shaft. The feedroll has an outer periphery with a circumferential groove. A bore in the feedroll is concentric with the outer periphery and fits snugly over the shaft. The feedroll also has a radial through slot opening into the bore and extending axially the full length of the feedroll. By aligning the through slot with the pin, the feedroll is able to slide over the shaft toward the wire feeder housing to be between the pin and the housing.
The feedroll also has a blind radial slot that opens into the bore. The blind slot is at the end of the feedroll that is opposite the wire feeder housing. By rotating the feedroll on the shaft until the blind slot is aligned with the pin, the feedroll can be slid away from the wire feeder housing such that the blind slot engages the pin. The spring is placed between the feedroll and the housing to hold the feedroll in engagement with the pin. If desired, the pin can protrude diametrically from opposite sides of the shaft. In that case, there are two opposed through slots and two opposed blind slots in the feedroll.
When the feedroll has worn, it is necessary merely to push it toward the wire feeder housing against the spring until the blind slot is disengaged from the pin. The feedroll is then rotated on the shaft until the through slot is aligned with the pin. The feedroll is slid off the shaft and replaced with a new feedroll.
According to one aspect of the invention, the feedroll has two circumferential grooves for different size weld wires and a blind slot on both ends. When a different size weld wire is to be used, the feedroll is removed from the shaft. It is then reversed end-for-end and replaced on the shaft.
A modified embodiment of the invention accommodates any end play in the wire feeder shaft. The shaft includes a shoulder, such as a snap ring, close to the wire feeder housing. The spring contacts the shoulder instead of the housing. In that manner, the shaft and feedroll are free to float through the shaft end play. When the weld wire is laid in the feedroll groove, the feedroll and shaft float into proper alignment with the rest of the weld wire guide system.
The method and apparatus of the invention, using a combination of through and blind slots in a feedroll, thus simplifies the task of replacing worn feedrolls. No tools are needed for the replacement process, even though the feedroll is positively held on the shaft both axially and angularly.
Other advantages, benefits, and features of the present invention will become apparent to those skilled in the art upon reading the detailed description of the invention.